In recent years the use of shipping containers has virtually revolutionized the freight handling industry, especially for international shipments, because of the convenience and economic advantages accruing from the use of weather-proof containers of rectangular shape which are capable of storing a number of unit items, where the packages of material, while confining and protecting the contents from loss or damage during transport as a unitary load, can be separated from the means of transport and trans-shipped without rehandling the contents.
In this connection, standardized containers (I.S.O. STANDARD) are standardized handling equipment have been developed concurrently to reap the maximum benefit from this development. Large numbers of now I.S.O. Standard Shipping Containers having a corner fitting at each corner thereof similar in general nature to that found in the I.S.O. Standard Shipping Containers. Some of these containers consist merely of frames having corner fittings mounted upon the corners of the frame. The corner fittings in most cases have orifices on the three outside faces thereof and the corner fittings are firmly attached to the body of the container. The function of the corner fitting is to provide an easily engageable reinforced means for connecting the containers to cranes, hoists, lashing devices and the like.
At this state, there is a world wide body of carriers, shippers, leasing companies, repair facilities, and manufacturers who are involved in the international intermodal transportation systems and who have an economic stake in assuring that the containers transported or serviced by them should be in compliance with the established standarads. These standards are based upon a container of forty foot length and having an end face approximately eight foot by eight foot and provide for use of shorter modules which can be arranged to occupy the space provided for a forty foot container in the hold of a ship or other intermodal transport.
As is well known in the arts, standard shipping containers or the type described have at each corner a corner fitting in which there is an orifice in each exterior face, each orifice opening into a common recess within the corner fitting. Many ships have been specifically adapted to carry containers. In the holds of these ships cells have been equipped and formed by a series of posts and the like wherein four rails have been created which are adapted to receive the corners of the containers which are forty feet long. In practice an average tolerance of 11/2 inches fore and aft and 1 inch athwart ships is incorporated in the cell so that the placement of the grooves of the cell permit ease of entry and removal of containers from the cell and the use of containers which are warped slightly dimensionally. The tolerance also permits lashing of containers to the deck of the hold of the ship. The containers are linked to each other vertically upon loading.
Ships loaded with containers stacked on top of each other in cells or lashed on deck, encounter problems when they sail on rough seas. The roll of the ship causes a column of containers vertically stacked in the hold thereof to be pressured by severe lateral inertial forces. I.S.O. and I.S.O. Type shipping containers are designed to withstand a lateral inertial force on the top end thereof of about 33,600 pounds without warping the container. However, experience has shown that containers are subjected to forces greatly in excess of that amount in actual use conditions on rough seas. These excesive forces have created severe damage to containers by warping the shape thereof and in some cases damage to the ships.
To overcome this problem, uses have resorted to lashing the individual containers in the stack to the deck. This solution is very difficult to achieve because the distances between the containers when set in position is very small. This makes the use of complex lashings and deck fittings mandatory. For example, in a area adapted to receive forty foot long containers when nominal twenty foot long containers are used in place of a forty foot long container in the space the twenty foot long containers are approximately one and a half inches short of being twenty feet and a space of three inches exists between the two faces of the twenty foot long containers. This limited clearance between opposing container ends makes it very difficult to lash them down to the deck. Further, if they are the top layer of a stack of containers five containers deep the lashing is over forty feet from the container top to the deck. Thus making if very hard to reinforce the container against damage caused by lateral inertial forces which are applied to the top of the container by the rolling motion of the ship.